Kinetics and particle size effects in ethene hydrogenation over supported palladium catalysts at atmospheric pressure

Palladium catalysts were synthesized in a highly controlled chemical vapor deposition process, giving narrowly distributed Pd nanoparticles with median sizes ranging from 1.3 to 5 nm on a SiO2 or TiO2 support. Unsupported Pd nanoparticles with median sizes between 3 and 9 nm were also generated by spark discharge. The influence of Pd particle size and support on the hydrogenation of ethene to ethane was investigated in a fixed-bed flow reactor at atmospheric pressure. The TOF was found to peak at 3 to 4 nm with a weak dependence on the support material. Metal support interactions were generally weak, indicated by closely matching activation energies of 20 kJ mol(-1) for unsupported Pd, and 28 kJ mol(-1) for titania and silica supported catalysts. Peak TOF values varied systematically with H-2 partial pressure, indicating a pronounced volume effect of the Pd particles on the reactivity. (C) 2009 Elsevier Inc. All rights reserved.